Zpat

My Feedback: (2)

Can someone tell me the current draw of a standard futaba servo. 3003, 3004, 148.
While flying last night I checked my battery with an Ace ESV and put the "standard" 250 mah draw on it. The needle went into the red, so I packed up, went home, and put the battery on the Digipace. It took 100 minutes to drain it.
I can't find any information on what the digipace draws and don't know what the servos would draw in full throttle, full control surface deflection.
Can someone please enlighten me?

Rodney

With no load on the servo, it should be drawing about 7 to 12 milliamperes at rest. As soon as a command to move it occurs, the current will jump to a higher value. How high? depends on the load but can easily approach 1 ampere for a fraction of a second. Now if the servo is stalled (movement blocked in some manner) or a very high amount of friction, this high current can persist until the load is removed or the brushes burn out or an electrical component fails due to overstress or heat. It may help you to dissconnect all servos from the receiver and then connect just one at a time while monitoring the current. When you find the sero(s) that cause the high current draw, you can further trouble shoot to see why that is happening.

Zpat

My Feedback: (2)

Rodney,
Thanks for the information. I understand the current will vary according to the loads imposed on the servo.
What I don't understand is the arbitrary 250 ma draw on the ESV. (Expanded Scale Voltmeter)
The ESV provides me with a 250 ma and a 500 ma load. With a 250 ma draw on the standard 4.8v, 500-600 mah battery pack my ESV pulled the voltage below the 4.8 limit. I then put it on a Digipace battery cycler to draw it down to see what was left in it. It cycled out at 100 minutes but I have no idea what kind of load the Digipace 1 imposes on the pack.
Does this mean I could have flown another 100 minutes or does it mean I can turn the radio on and it will be good for 100 minutes at idle
So I guess my question would be, what is the draw of a Digipace 1 and what does the 100 minute reading actually mean?

Rodney

I miss interpreted your first post. If you mean that only when you put the ESV with a 250 milliamp load on the system, the meter reads below acceptable limits yet the battery (on a separate tester) checks out with more than ample milliamperehours left; then I suspect that your planes wiring has a high impedance somewhere, most probably in the switch or one of the connectors to the battery or switch. Try bypassing the old switch assembly and wiring with a known good one and see if you get the same response. There seems to be a definite voltage drop somewhere between your ESV and the battery. If so, this could also cause serious problems in flight.

JohnBuckner

My Feedback: (1)

No that 100 minutes indication is how long it will take to draw the battery down down to 1.1v per cell (total safe discharge) and that is way below the safe operating voltage of the flight system.

The Digipace 2 has a selectable applied load of either 350 or 500 milliamps. I don,t know load or loads used in the Digipace 1 or 3

Zpat

My Feedback: (2)

I just finished giving the above battery pack a full charge and have it in the airplane. It has a static reading of approximately 5.6 volts. When I apply a 250 ma load with the ESV the voltage drops to 5.4.
I believe when I oringinally checked the battery last night the stactic reading was 5.1 volts and at a 250 ma draw it was about 4.75 volts.
I found the instructions for the Digipace and it discharges at a 300 mah rate.

Does this mean at 5.1 volts I can figure about another hour of flight time, since the complete discharge at 300 ma took 100 minutes?
How does this reasoning sound to you guys?
Thank for the info.

Zpat

My Feedback: (2)

Can anybody answer my last question or are there too many variables?

ZAGNUT

My Feedback: (1)

too many variables...unless you know for sure that you only draw 300mA or less during flight

try this: connect an ammeter to your planes battery, tape the plane to the roof of your car and fiddle with the TX sticks while driving at the approximate speed that your plane flies....ignore the looks you get from other drivers


dave

FHHuber

Available flying time on the (1 2/3 hr X 300 ma/h = appx 500 mah) that remained in your pack is debateable.

My .91 4-stroke powered Tiger 60 seemed to average 60 ma/min power drain from the RX pack last time I flew it. (from the results of field charging with a charger that tells how much it put back in the pack.) I imagine that it has a lot to do with the style of flying I was doing, which is mostly SMOOTH 1/2 throttle stuff. I've DRAINED a fully charged 1800 mah pack with the same airplane in 1 hour of flying (nearly 5 times the discharge rate!) when doing nearly constant full throttle aerobatics.

Zpat

My Feedback: (2)

Thanks for the information . I think I'll explore this.

Keefer

My Feedback: (2)

Batteries have internal resistance - as the current flowing through a battery goes up, the internal resistance will cause the battery voltage to drop. If you're dropping below something like 4.2v on a 4-cell pack, I think that's where you start worrying about servos stalling. For instance, a pack that's already low (4.7 v, say) in a plane in a dive... pull the elevator to full travel and the air drag pushes hard against the elevator - current draw by that servo goes way up, as does the current through the battery - battery voltage drops, and as it goes below 4.2 (or some low value - the techies will correct me I'm sure), the servo starts to lose torque, the elevator tends to flatten out due to air pressures, and plane never pulls out of the dive....

mr.rc-cam

The NiCd discharge curves are determined by the cell MFG using a C/5 load. I suspect that some ESV's just assume that 600mAH cells are being used and determine their finger-in-wind cutoff voltages (red zone) when their fixed load is used.

There is no way to easily determine the battery's remaining mAH from the voltage. Other trickery is needed to do that properly.